The present invention relates to an apparatus and method for providing a mobile radio communication system, particularly one of small capacity and particularly one which can operate close to a source of interference. The source of interference may be, for instance, a cellular telephone system or a point-to-point microwave source. The present invention also relates to a base transceiver station and a mobile station and methods of operating the same. The present invention may be applied to a microzone mobile telephone system including at least one base station and method of operating the same. The present invention is particularly suited for the operation of a microcellular system within a building.
U.S. Pat. No. 4,790,000 describes a private mobile telephoned system associated with a building which re-uses frequencies allocated to a larger public cellular telephone system in which it lies. The private system uses frequencies which are allocated to the immediately adjacent cell of the public system.
U.S. Pat. No. 5,142,691 describes a wireless packet communication system, e.g. in within a building, which shares frequencies with other radio systems. The proposed wireless system includes means for locking the transmitter in the system when a scan indicates that at least one of the frequencies for use in the wireless system would interfere with the other radio system.
U.S. Pat. No. 5,276,908 describes a base station and a mobile station of a radio communication system both of which scan frequencies to identify frequencies used by fixed radio transmission services on a call-by-call basis. The channel for communication in the radio communication network is selected based on this scan.
U.S. Pat. No. 5,142,658 describes a detection method for a wireless communication system for detecting beacons from point-to-point microwave system. The signal strength from observed beacons is measured at both the base station and the mobile station and the frequency for communication within the wireless system is based on the measurements.
U.S. Pat. No. 5,459,727 describes a microzone mobile telephone system of low transmission power. The proposal is intended for use as an adjunct to a wired telecommunications system such as a PBX. No provisions are made to prevent disturbance from a larger overlapping cellular system. If any such disturbance should occur it is assumed that sophisticated error correction schemes compensate for the interference.
U.S. Pat. No. 5,402,523 describes a microzone mobile telephone system within a larger cellular network. A detector in the microzone system detects radio signals within one frequency band used in the overlapping larger network. The detector also estimates the disturbance risk caused by the larger network in the microzone network and the disturbance risk caused by microzone transmissions in the larger network. The detector attempts to allocate frequencies or to change to frequencies in the microzone network which cause the least disturbance.
U.S. Pat. No. 5,581,597 describes a radio personal communications system operating in a wide area cellular system. A base station within the personal communications system is allocated a frequency for communication by the wide area cellular system.
U.S. Pat. No. 5,448,750 describes a spectrum sharing system for monitoring available spectrum shared between a mobile radio communications network and incumbent radio stations. The system includes directional monitoring antennae which are located around a microcell for monitoring interfering signals from the incumbent radio stations.
U.S. Pat. No. 5,625,672 also describes a microzone mobile telephone system within a larger cellular network. The microzone system uses the same frequency band and channels as the larger network. A monitoring receiver in the microzone system detects radio signals within the frequency band used by the overlapping larger network and makes those channels which are less likely to interfere with the cellular network available to the microzone system.
Both the latter two known microzone systems require at least one monitoring receiver in addition to communications transceivers within the microzone system which adds expense to the microzone system. One problem with such systems is that the frequencies used for transmission in the microcellular system jam the receivers of the same system which are trying to monitor the activity of radio sources outside the microcellular system. ""750 solves this problem by using directional antennae whose direction of reception points away from the microcell in question. Such a system is complex, requiring additional specialized antennae and receiver and analyzer electronics.
In the article xe2x80x9cThe wireless officexe2x80x9d by Gordon J. Povey in Electronics and Communication Eng. Journal, vol. 8, no. 2, April 1996, the concept is described of providing cellular phones to employees for general use within an office building rather than the employees having conventional wire-line telephones. Low power base stations are used in the office and the cellular phones are said to be compatible with the main cellular network outside the building. This suggestion has been criticized in the article by W. H. W. Tuttlebee entitled xe2x80x9cCordless telephones and cellular radio: synergies of DECT and GSMxe2x80x9d, Electronics and Communication Eng. Journal, vol. 8, no. 5, October 1996, as being too expensive. The alternative solution of using a cordless telephone system within the office (e.g. DECT, Digital Enhanced Cordless Telecommunications) and a cellular system outside requires either two separate mobile telephones which operate in the respective systems, or a dual handset which can switch from the indoor cordless system to an outdoor cellular system. Such a system is proposed in U.S. Pat. No. 5,594,782.
There remains a requirement to provide an inexpensive mobile telephone system which may be 100% compatible with an adjacent cellular network and which allows, for example, a xe2x80x9cwireless officexe2x80x9d to be retro-fitted economically within an existing larger cellular system and without causing, or being subject to, disturbance from the cellular system. The wireless office could be, for instance, a factory or a university campus. Further, there is a requirement to be able to operate a mobile telephone system within a larger cellular system on a temporary basis, e.g. within the temporary field headquarters of an emergency operation, e.g. after a major earthquake or at an industrial fair.
It is an object of the present invention to provide a mobile radio communications system which can operate close to a source of interference, e.g. a cellular system, a microwave source or a radar scanner.
It is still a further object of the present invention to provide a mobile radio communications system which is compatible with adjacent cellular systems.
It is still a further object of the present invention to provide a lower cost microzone mobile radio communications system and a method of operating the same.
The present invention includes a cellular mobile radio communication system comprising:
at least one cell; and each base station transceiver within said cell including means for at least temporarily transmitting signals discontinuously on a beacon frequency.
The present invention also includes a mobile radio communication system comprising:
a base station transceiver including means for transmitting signals within a frequency band to one or more mobile stations and means for receiving signals, said base station receiver also including:
means for at least temporarily interrupting the transmission of signals on a beacon frequency from said base station receiver; and
means for monitoring signals received by said base transceiver station in said frequency band while said beacon frequency transmission is interrupted.
The present invention also includes a mobile radio telecommunication system base transceiver, comprising:
means for transmitting signals within a frequency band and means for receiving signals, and
means for at least temporarily interrupting the transmission of signals on a beacon frequency from said base transceiver station, and means for monitoring signals received by said base transceiver in the frequency band while said beacon frequency transmission is interrupted.
The present invention also includes a method of operating a cellular mobile radio communication system comprising the step of:
at least temporarily transmitting a beacon frequency discontinuously within at least one cell.
The present invention also includes a method of operating a mobile radio communication system comprising the steps of:
transmitting signals from a base station transceiver within a frequency band to one or more mobile stations;
receiving signals at said base station transceiver;
at least temporarily interrupting the transmission of signals on a beacon frequency from said base station receiver; and
monitoring signals received by said base transceiver in said frequency band while said beacon frequency transmission is interrupted.
The present invention also includes a method of operating a mobile radio telecommunication system base transceiver, comprising the steps of:
transmitting signals within a frequency band to one or more mobile stations; receiving signals;
at least temporarily interrupting the transmission of signals on a beacon frequency; and monitoring signals received by said base transceiver station in said frequency band while said beacon frequency transmission is interrupted.
The present invention also includes a mobile station for use with a mobile radio communication system in which a beacon frequency is at least temporarily transmitted discontinuously, comprising:
means for selective measurement of a characteristic of received radio signals only when said beacon frequency is transmitted.
The method or station or system in accordance with the present invention is particularly suitable for use with a TDMA system such as the GSM system.
The present invention may provide the advantage that a microzone system transmits at a low power so that it does not disturb surrounding radio frequency users. Further, in accordance with the present invention, such a microzone system can monitor the beacon frequencies of surrounding radio frequency users and select frequencies which will not cause interference. Still a further advantage is that when a base transceiver station is not transmitting the beacon frequency it may transmit on other frequencies, e.g. it can perform slow frequency hopping, thus increasing the efficiency of small transceivers which do not need to have one transceiver merely to fill the slots on the beacon frequency. Further, in accordance with the present invention the time slot occupancy on the beacon frequency (duty cycle) may be adjusted optimally for the required cell capacity.
The dependent claims define individual further embodiments of the present invention.
The invention and its advantages and embodiments will be described with reference to the following drawings.